<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .container {
            border:1px solid #ccc;
            width:100%;
            text-align: center;
        }
        .child {
            display: inline-block;
            width:20%;
            height:200px;
            border:1px solid greenyellow;
        }
        .pdh {
            padding:30px;
            margin:30px;
        }
        .border-size {
            box-sizing: border-box;
        }
    </style>
</head>
<body>
<div class="container">
    <div class="child pdh mgh">
        <code>
            padding: 30px;<br>
            margin: 30px;<br>
        </code>
    </div>
    <br>
    <div class="child">
        <code>
            padding: 0;<br>
            margin: 0;<br>
        </code>
    </div>
    <br>
    <div class="child pdh mgh border-size">
        <code>
            padding: 30px;<br>
            margin: 30px;<br>
            box-sizing: border-box;<br>
        </code>
    </div>
</div>
</body>
</html>
